Feeds and feeding regimes - grouper

As with all culture systems, there are many local variations in the feeds and feeding regimes utilized. There appears to be no universal system, and local availability seems to be the key criteria in developing a feeding schedule. Fry and fingerlings are fed with mysids and small shrimp for a couple of days post-catching in tanks, to acclimatize them and check that all individuals are eating.

Trash fish forms the main feed in nursery and production cages, which is minced or chopped to suit each size group; trash fish may be supplemented with vitamins and minerals. This kind of feed is gradually being replaced by moist pelleted feed.
A suitable starter feed for groupers should contain 50-60% high quality protein, 12-16% fat, ?15% carbohydrate, ?3% fibre and ?16% ash (Tucker 1999). Lower quality feeds may result in higher feed conversion ratios (FCR) and possibly slower growth. In grow-out cages, fish are fed at 10% of body weight daily, while those in nursery cages are given about 8% of body weight/day.

The optimum feeding rate in production cages is 5% of body weight and the range of FCRs achieved is 0.94 to 7.5:1, depending on the feed and the species (Pillay 1995; Boonyaratpalin 1997; Bombeo-Tuburan, Kanchanakhan and Chinabut 2001). According to Agbayani (2002) FCRs average between 2.5-2.8:1 for dry pellets and 6.3:1 for trash fish. When temperatures fall below 15°C, the fish do not feed. Some species of groupers feed indifferently during the day or night; others (for example Epinephalus akaara) favour feeding just before sunset. Cultured red groupers exhibit a special feeding behaviour: the fish can be trained to know when to expect food. When they sense the sound of trash fish being chopped or a wooden plank being knocked, they gather at the cage edge. As groupers are of a suspicious nature, they watch for food but do not move. However, if one fish attempts to approach the food, all the fish will immediately attack it violently, sometimes injuring themselves in the process. Groupers usually eat one to three pieces of minced trash fish, then disperse. No attempts are ever made to eat any food which falls to the net bottom, no matter how hungry the groupers might be. Owing to this special feeding behaviour, groupers are generally reared with seabream which act as scavengers and stimulate the groupers to feed (Boonyaratpalin 1997). This is also a means of preventing water pollution due to decaying feed.
Trash fish is commonly used for feeding in grouper cage culture, but its increasing cost, shortage of supply, variable quality and poor feed conversion ratios indicate that this form of feed may not be the best from either a nutritional or an economic point of view. However, groupers fed with bycatch (trash fish) in a study by Bombeo-Tuburan, Kanchanakhan and Chinabut (2001) fared significantly better in terms of final length and total production than when fed other diets (live tilapia, formulated diet). The quality of the bycatch used may be estimated from the efficient feed conversion achieved (1:1 on dry basis), significantly better than the formulated diet, which had an FCR of 2.8. Using bycatch, 47% of the harvest weighed more than 400 g, with only 14% being classified as <200 g.
A major problem is the limited supply of trash fish, so there is a need to develop a suitable diet for grow-out grouper production (Millamena 2002). Fishery products, either in the form of low value trash fish or fishmeal, are presently the major sources of protein in the grow-out culture of most fish species and constitute up to 70% of their dietary composition (Tacon 1995). As the demand for fishmeal and fish oil for aquaculture increases, costs are expected to rise unless new sources (e.g. fish discards; krill; mesopelagics) can be economically exploited or substitutes for these marine products for inclusion in aquafeeds prove commercially applicable (New and Wijkstrom 2002).
A dependable supply of cost-effective, non-marine, sources of alternative protein must be provided if fish farming is to remain profitable. Millamena (2002) conducted a feeding trial to evaluate the potential of replacing fishmeal with processed animal by-product meals, meat meal and blood meal, in practical diets for juvenile groupers (Epinephelus coioides). The study demonstrated that up to 80% of fishmeal protein can be replaced by processed meat meal and blood meal derived from terrestrial animals with no adverse effects on growth, survival, and FCR. From an economic standpoint, replacement of fishmeal with cheaper animal by-product meals in practical diets can alleviate the problem of low fishmeal availability and high costs. These processed by-products can be delivered in the Philippines, for example, at US$ 0.40/kg, less than half the price of most commercial fishmeals (US$ 1/kg). The effective use of meat meal-based diets for grouper grow-out also reduces the requirements for trash fish, another fishery resource that is extensively used (Millamena 2002). Economic sensitivity analysis showed that a combination of improvements resulted in higher return-on-investment (ROI). However, these apparently favourable results must be balanced with the fact that some countries (e.g. in the EU) have banned the inclusion of all terrestrial meat-meal based products in fish feeds, due to fears concerning the linkage between the mad-cow disease (BSE) and CJD in humans.